1,278 research outputs found
Redshifts of the Gravitational Lenses MG1131+0456 and B1938+666
The redshifts of the gravitational lens galaxies in MG1131+0456 and B1938+666
are 0.844 and 0.881 respectively. Both are early-type galaxies lying at the
redshifts predicted by assuming that they are early-type galaxies with old
stellar populations lying on the fundamental plane. We also find evidence for a
foreground group of galaxies at z=0.343 near MG1131+0456. The source redshifts
are predicted to be >1.8 in both systems, but they are so red that infrared
spectra will be required to determine their redshifts.Comment: 10 pages, AASTeX Latex, including 1 JPEG and 2 postscript figures,
submitted to Astronomical Journal Minor typos fixe
The 8 o'clock Arc: A Serendipitous Discovery of a Strongly Lensed Lyman Break Galaxy in the SDSS DR4 Imaging Data
We report on the serendipitous discovery of the brightest Lyman Break Galaxy
(LBG) currently known, a galaxy at z=2.73 that is being strongly lensed by the
z=0.38 Luminous Red Galaxy (LRG) SDSS J002240.91+143110.4. The arc of this
gravitational lens system, which we have dubbed the "8 o'clock arc" due to its
time of discovery, was initially identified in the imaging data of the Sloan
Digital Sky Survey Data Release 4 (SDSS DR4); followup observations on the
Astrophysical Research Consortium (ARC) 3.5m telescope at Apache Point
Observatory confirmed the lensing nature of this system and led to the
identification of the arc's spectrum as that of an LBG. The arc has a spectrum
and a redshift remarkably similar to those of the previous record-holder for
brightest LBG (MS 1512-cB58, a.k.a "cB58"), but, with an estimated total
magnitude of (g,r,i) = (20.0,19.2,19.0) and surface brightness of
(mu_g,mu_r,mu_i) = (23.3, 22.5, 22.3) mag/arcsec^2, the 8 o'clock arc is thrice
as bright. The 8 o'clock arc, which consists of three lensed images of the LBG,
is 162deg (9.6arcsec) long and has a length-to-width ratio of 6:1. A fourth
image of the LBG -- a counter-image -- can also be identified in the ARC 3.5m
g-band images. A simple lens model for the system assuming a singular
isothermal ellipsoid potential yields an Einstein radius of 2.91+/-0.14 arcsec,
a total mass for the lensing LRG (within the (10.6+/-0.5)/h kpc enclosed by the
lensed images) of 1.04x10^12/h Msun, and a magnification factor for the LBG of
12.3(+15/-3.6). The LBG itself is intrinsically quite luminous (approximately
6L*) and shows indications of massive recent star formation, perhaps as high as
160/h Msun/year.Comment: 4 pages 5 figures, submitted to ApJ Letter
The Cut & Enhance method : selecting clusters of galaxies from the SDSS commissioning data
We describe an automated method, the Cut & Enhance method (CE) for detecting
clusters of galaxies in multi-color optical imaging surveys. This method uses
simple color cuts, combined with a density enhancement algorithm, to up-weight
pairs of galaxies that are close in both angular separation and color. The
method is semi-parametric since it uses minimal assumptions about cluster
properties in order to minimize possible biases. No assumptions are made about
the shape of clusters, their radial profile or their luminosity function. The
method is successful in finding systems ranging from poor to rich clusters of
galaxies, of both regular and irregular shape. We determine the selection
function of the CE method via extensive Monte Carlo simulations which use both
the real, observed background of galaxies and a randomized background of
galaxies. We use position shuffled and color shuffled data to perform the false
positive test. We have also visually checked all the clusters detected by the
CE method. We apply the CE method to the 350 deg^2 of the SDSS (Sloan Digital
Sky Survey) commissioning data and construct a SDSS CE galaxy cluster catalog
with an estimated redshift and richness for each cluster. The CE method is
compared with other cluster selection methods used on SDSS data such as the
Matched Filter (Postman et al. 1996, Kim et al. 2001), maxBCG technique (Annis
et al. 2001) and Voronoi Tessellation (Kim et al. 2001). The CE method can be
adopted for cluster selection in any multi-color imaging surveys.Comment: 62 pages, 32 figures, Accepted for publication in the Astronomical
Journal, "the CE galaxy cluster catalog can be downloaded from,
http://astrophysics.phys.cmu.edu/~tomo/ce/
Kebiasaan Makan Balita Stunting Pada Masyarakat Suku Sasak: Tinjauan 1000 Hari Pertama Kehidupan (HPK)
The first 1000 days of a child's life is the most crucial period for child's cognitive and mental development. The lack of nutrition in the period would cause inter-generation shortness, known as stunting. Moreover, stunting could lead to brain cells development and increase the risk of degenerative disease. The phenomena was mostly found in Central Lombok with high pervelance of stunting in toddler. This research uses qualitative approach with phenomenology research design; conducted in Community Health Center (Pusat Kesehatan Masyarakat/Puskesmas) in Sengkol, District of Central Lombok. This article concludes that there are diatery habit in Sasak people which became predisposing factors to the occurrence of stunting to the children in Sasak. Those are the lack of animal protein intake, mistreatment of breast milk pattern giving which causes failure to fulfill nutrition standard, and there are myth-related belief that opposes the principal of nutrition fulfillment in children
The Northern Sky Optical Cluster Survey II: An Objective Cluster Catalog for 5800 Square Degrees
We present a new, objectively defined catalog of candidate galaxy clusters
based on the galaxy catalogs from the Digitized Second Palomar Observatory Sky
Survey (DPOSS). This cluster catalog, derived from the best calibrated plates
in the high latitude (|b|>30) Northern Galactic Cap region, covers 5,800 square
degrees, and contains 8,155 candidate clusters. A simple adaptive kernel
density mapping technique, combined with the SExtractor object detection
algorithm, is used to detect galaxy overdensities, which we identify as
clusters. Simulations of the background galaxy distribution and clusters of
varying richnesses and redshifts allow us to optimize detection parameters, and
measure the completeness and contamination rates for our catalog. Cluster
richnesses and photometric redshifts are measured, using integrated colors and
magnitudes for each cluster. An extensive spectroscopic survey is used to
confirm the photometric results.
This catalog, with well-characterized sample properties, provides a sound
basis for future studies of cluster physics and large scale structure.Comment: 49 pages, 16 figures. Accepted to AJ; appearing in April. Version
with full resolution figures, and full length tables available at
http://dposs.caltech.edu:8080/NoSOCS.htm
Galaxy-Quasar correlations between APM galaxies and Hamburg-ESO QSOs
We detect angular galaxy-QSO cross-correlations between the APM Galaxy
Catalogue and a preliminary release (consisting of roughly half of the
anticipated final catalogue) of the Hamburg-ESO Catalogue of Bright QSOs as a
function of source QSO redshift using multiple cross-correlation estimators.
Each of the estimators yield very similar results, implying that the APM
catalogue and the Hamburg-ESO survey are both fair samples of the respective
true galaxy and QSO populations. Though the signal matches the expectations of
gravitational lensing qualitatively, the strength of the measured
cross-correlation signal is significantly greater than the CDM models of
lensing by large scale structure would suggest. This same disagreement between
models and observation has been found in several earlier studies. We estimate
our confidence in the correlation detections versus redshift by generating 1000
random realizations of the Hamburg-ESO QSO survey: We detect physical
associations between galaxies and low-redshift QSOs at 99% confidence and
detect lensing associations at roughly 95% confidence for QSOs with redshifts
between 0.6 and 1. Control cross-correlations between Galactic stars and QSOs
show no signal. Finally, the overdensities (underdensities) of galaxies near
QSO positions relative to those lying roughly 135 - 150 arcmin away are
uncorrelated with differences in Galactic extinction between the two regions,
implying that Galactic dust is not significantly affecting the QSO sample.Comment: 35 pages total, including 9 figures. Accepted by the Astrophysical
Journa
SDSS-RASS: Next Generation of Cluster-Finding Algorithms
We outline here the next generation of cluster-finding algorithms. We show
how advances in Computer Science and Statistics have helped develop robust,
fast algorithms for finding clusters of galaxies in large multi-dimensional
astronomical databases like the Sloan Digital Sky Survey (SDSS). Specifically,
this paper presents four new advances: (1) A new semi-parametric algorithm -
nicknamed ``C4'' - for jointly finding clusters of galaxies in the SDSS and
ROSAT All-Sky Survey databases; (2) The introduction of the False Discovery
Rate into Astronomy; (3) The role of kernel shape in optimizing cluster
detection; (4) A new determination of the X-ray Cluster Luminosity Function
which has bearing on the existence of a ``deficit'' of high redshift, high
luminosity clusters. This research is part of our ``Computational
AstroStatistics'' collaboration (see Nichol et al. 2000) and the algorithms and
techniques discussed herein will form part of the ``Virtual Observatory''
analysis toolkit.Comment: To appear in Proceedings of MPA/MPE/ESO Conference "Mining the Sky",
July 31 - August 4, 2000, Garching, German
Improved constraints on H0 from a combined analysis of gravitational-wave and electromagnetic emission from GW170817
The luminosity distance measurement of GW170817 derived from GW analysis in
Abbott et al. 2017 (here, A17:H0) is highly correlated with the measured
inclination of the NS-NS system. To improve the precision of the distance
measurement, we attempt to constrain the inclination by modeling the broad-band
X-ray-to-radio emission from GW170817, which is dominated by the interaction of
the jet with the environment. We update our previous analysis and we consider
the radio and X-ray data obtained at days since merger. We find that the
afterglow emission from GW170817 is consistent with an off-axis relativistic
jet with energy
propagating into an environment with density , with preference for wider jets (opening angle
deg). For these jets, our modeling indicates an off-axis angle deg. We combine our constraints on with the
joint distance-inclination constraint from LIGO. Using the same
km/sec peculiar velocity uncertainty assumed in A17:H0 but with an inclination
constraint from the afterglow data, we get a value of \mbox{km/s/Mpc}, which is higher than the value of
\mbox{km/s/Mpc} found in A17:H0. Further,
using a more realistic peculiar velocity uncertainty of 250 km/sec derived from
previous work, we find km/s/Mpc for H0 from
this system. We note that this is in modestly better agreement with the local
distance ladder than the Planck CMB, though a significant such discrimination
will require such events. Future measurements at days of the
X-ray and radio emission will lead to tighter constraints.Comment: Submitted to ApJL. Comments Welcome. Revised uncertainties in v
Merging Galaxies in the SDSS EDR
We present a new catalog of merging galaxies obtained through an automated
systematic search routine. The 1479 new pairs of merging galaxies were found in
approximately 462 sq deg of the Sloan Digital Sky Survey Early Data Release
(SDSS EDR; Stoughton et al. 2002) photometric data, and the pair catalog is
complete for galaxies in the magnitude range 16.0 <= g* <= 20.
The selection algorithm, implementing a variation on the original
Karachentsev (1972) criteria, proved to be very efficient and fast. Merging
galaxies were selected such that the inter-galaxy separations were less than
the sum of the component galaxies' radii.
We discuss the characteristics of the sample in terms of completeness, pair
separation, and the Holmberg effect. We also present an online atlas of images
for the SDSS EDR pairs obtained using the corrected frames from the SDSS EDR
database. The atlas images also include the relevant data for each pair member.
This catalog will be useful for conducting studies of the general
characteristics of merging galaxies, their environments, and their component
galaxies. The redshifts for a subset of the interacting and merging galaxies
and the distribution of angular sizes for these systems indicate the SDSS
provides a much deeper sample than almost any other wide-area catalog to date.Comment: 58 pages, which includes 15 figures and 6 tables. Figures 2, 8, 9,
10, 11, 13, and 14 are provided as JPEG files. For online atlas, see
http://home.fnal.gov/~sallam/MergePair/ . Accepted for publication in A
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